With the development of the semiconductor manufacturing technology, technical nodes have consistently decreased, the high-K/metal gate technology have been widely used. A desired threshold voltage has been obtained by forming a metal layer with a different work function between the high dielectric constant (high-K) dielectric layer and the metal gate structure of the high-K/metal gate structure. However, when the critical dimension (CD) is further reduced, the structures of conventional MOS field effect transistors (MOSFETs) are unable to match requirements of the device performance. Fin field-effect transistors (FinFET) have attracted extensive attentions because they may substitute the conventional devices.
FIG. 1 illustrates an existing FinFET. As show in FIG. 1, the FinFET includes a semiconductor substrate 10 and a protruding fin 14 formed on the semiconductor substrate 10. The fin 14 may be formed by etching the semiconductor substrate 10. The FinFET also includes a first dielectric layer 11 covering a surface of the semiconductor substrate 10 and a portion of side surfaces of the fin 14, and a metal gate structure 12 stretching across the fin 14 and covering the top and side surfaces of the fin 14. The metal gate structure 12 includes a high-K dielectric layer (not shown) on the side and top surface of the fin 14; a metal gate electrode (not shown) formed on the high-K dielectric layer; and a second dielectric layer (not shown) covering the first dielectric layer 11 and the fin 14. The surface of the second dielectric layer levels with the surface of the metal gate structure 12.
However, when the technical node of the FinFET is further reduced, the performance of the FinFET may need further improvement. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.